Antenna system



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ANTENNA SYSTEM Original Filed Jan. 28, 1937 Transmiffer Trans/m HerINVENTOR H. o. PETERSON ATFORNEY avwggw wr lengths, such as the earthpath and the sky path.

Patented Oct. 8, 1940 UNITED STATES ANTENNA SYSTEM Harold 0. Peterson,Riverhead, N. Y., assignor to Radio Corporation of America, acorporation of Delaware Original application January 28, 1937, ,SerialNo. 122,699. Divided and thisapplication March 30, 1939, SerialNo.264,905

Claims.

This invention relates to antenna systems and, more particularly, totransmitting antennas for radiating power at broadcast frequencies.

The present application is a division of application No. 122,699, filedJanuary 28, 1937, in the United States Patent OfIice.

One common cause of interference at a receiver results from therecombination of waves arriving at a receiver over paths of difierent Inthe earth path are components of the wave which are transmittedhorizontally, while in the sky paths are components which aretransmitted at a high angle of elevation and reflected back to the earthby the Heaviside layer. It has heretofore been proposed to overcome thisinterference by radiating waves at a low angle to the earth by employingone or more vertical transmitting antennadoublets, each having a lengthequal to half the length of the communication wave. At broadcastingfrequencies, however, in the range of wavelengths of 200 to 600 meters,it is impractical both from an expense standpoint and because of thegreat height involved to build a half wavelength vertical doublet. Y

-The present invention overcomesthe foregoing difficulties and providesa transmitting antenna system which givesrelatively low angle radiationwithout using structures of great height. More especially, the antennaof the invention comprises a plurality of horizontal wave antennas,-which are disposed radially with respect to a central point, and whichhave a length at least as long as half the length of the communicationwave. These antennas are at a relatively short distance above the earthand are designed each to produce maximum radiation in one direction,that is, in the direction away from the feeding point. Such waveantennas radiate vertically polarized waves, and maximum radiationoccurs at relatively low angles with respect to the earth.

A more detailed description of the invention follows in connection withthe accompanying drawing, wherein Figures 1 and 2 show two embodiments'of the invention, In these figures the same parts are represented by thesame reference numerals.

Referring to Figure 1, there is shown in plan View a transmittingantenna system constituted by a plurality of horizontal wave antennasdisposed radially with respect to a central feeding point. The waveantenna is well known per se,'

and is adequately described in United States Patent No. 1,381,089,granted June 7, 1921, to

Harold H. Beverage, to whichrefe rence is herein made. Each wave antennais designated by the reference numeral 5 and is fed through atransformer I from a central transformer 2 whose impedance is designedto match the impedance of the circuit to which it is connected. The primary winding of transformer 2 is coupled to a. transmission line 4 overwhich energy is fed from a transmitter 6. The far ends ofthe waveantennas 5 are damped, i. e., connected to earth, through surgeresistors 3 toprevent reflections. Inthi's manner, the flow ofenergyalong the wave antenna is in one direction. only and theindividual antenna is given 'a unidirectional transmittingcharacteristic. Antennas 5 are located at a height'above groundsomewhere between twenty feetand one hundred twenty feet, depending uponlocal conditions, such'as ground characteristics, height of trees, thecost of towers, and the length of thecommunication wave. The length ofeach antenna is dependent on'the directivity desired therefrom.Generally, a length for each antenna between one-half wavelength andthree wavelengths will be found satisfactory, although the exact lengthmust be determined by the conditions to be satisfied.

' Antennasi are so spacedas to give the desired result, and if it isdesired that radiationt'akei place in all directions, the spacingbetween antennas will generally be of the order of 60. Although withthis spacing there may be some overlapping between the adjacentradiation patterns of adjacent antennas, it will be found that becausethe invention employs the vertical polarization component of radiation,this com-' ponent from two overlapping antenna patterns will arrive atthe receiving point substantially in phase, and consequently nointerference will result therefrom; The angle of elevation in theradiated wave from each antenna will depend upon the length of the wireand upon the ground condition. It is preferred that the angle ofelevation be confined to something below '30? or 40 with respect toground.

Figure 2 discloses a modification of the arrangement of Figurev 1, anddiffers therefrom mainly in arranging the antennas to cross each othernear their midpoints. In this arrangement the antennas 5 are each fed atone end through transformers I, I over suitable transmission lines A, B,C, these lines being adjustable in length and connected to a commonfeeding point which is coupled to the transmitting apparatus 6 over line4. Suitable damping resistors 3 prevent refiections in the antennas inthe same manner as above described in connection with Figure 1. Theaverage phase of each of the antennas 5 is the phase of each of theirmidpoints. By a suitable adjustment of the phase at each of the feedpoints I by an adjustment of the lengths of transmission lines A, B, C,or otherwise, the average phase of each of the antennas may be made thesame at the exact geographical center. The polar diagram of the antennasystem in the horizontal plane will be much simplified due to theconsequent absence of interference patterns.

caused by geographical spacing of the-midpoints of the several antennacomponents.

It will be understood, of course, that if uniform radiation in alldirections is not desired, one or more antennas 5 may be eliminated fromthe system in the direction toward which it is not desired to transmit.Nor is the invention limited to the number of wave antennas shown, sincethis number will depend on such factors as the spacing, radiationpatterns from each antenna, etc.

What is claimed is:

1. An antenna arrangement comprising a plurality of horizontal antennas,each at least onehalf the length of the communication wave, saidantennas crossing each other at substantially their midpoints, highfrequency energy transducer means so coupled to each of said antennas atone end only that energy at all of said coupling points is in phase andmeans for preventing reflection from the ends of said antennas remotefrom the ends first mentioned whereby the directivity of said antenna isconfined to a low vertical angle.

2. A transmitting arrangement comprising a plurality of horizontalantennas, each at least one-half the length of the communication wave,said antennas crossing each other at substantially their mid-points,means for so energizing said antennas, each from one end only, that theenergy therein is in phase at their mid-points and means for preventingreflection from the ends of each of said antennas remote from the endsfirst mentioned whereby radiation is obtained from said antennas atsubstantially low angles.

3. A transmitting arrangement comprising a plurality of horizontal waveantennas, each at least one-half the length of the communication wave,said antennas crossing each other at substantially their mid-points,means for so energizing said antennas at one of each of their ends thatthe energy therein is in phase at their mid-points and means forpreventing reflection from the other ends of each of said antennaswhereby radiation is obtained from said antennas at substantially lowangles.

4. A transmitting antenna arrangement comprising a plurality ofhorizontal antennas, each at least one-half the length of thecommunication wave whereby maximum radiation from each of said antennastakes place in a direction along the direction of said antennas, theexact length of each of said antennas being such that the angle ofradiation with respect to the horizontal is below 40 degrees, saidantennas crossing each other at substantially their mid-points, meansfor so energizing said antennas, each from one end only, that the energytherein is in phase at their 'midpoints and means providing a surgeimpedance at the ends of said antennas remote from the ends firstmentioned for preventing reflection of waves along said antennas, theradial spacing between adjacent antennae being such that substantiallyequal radiation takes place in all directions.

5. A transmitting antenna arrangement comprising a plurality ofhorizontal antennas, each at least one-half the length of thecommunication wave whereby maximum radiation from each of said antennastakes place in a direction along the direction of said antennas, theexact length of each of said antennas being such that the angle ofradiation with respect to the horizontal is below 40 degrees, saidantennas crossing each other at substantially their mid-points, meansfor so energizing each of said antennas from one end only that theenergy therein is in phase at their midpoints and means providing asurge impedance at the ends of each of said antennas remote from theends first mentioned for preventing reflection of waves along saidantennas, the radial spacing between adjacent antennae being generallyof the order of 60 degrees whereby equal radiation takes place in alldirections.

HAROLD O. PETERSON.

